The prior art has many showings of piston-type pump dispensers in which a metal spring is compressively disposed inside the cylinder, biasing the piston toward the position of maximum volume. The vertical pump shown in the McKinney patent above is a good example of such an arrangement.
In some pumps of the prior art where the liquid product being dispensed is corrosive as, for instance, bleach, the metal spring is in the cylinder with the liquid and subject to attack. For this reason some pumps of various types have moved the metal spring to the outside of the cylinder.
Rubber biasing members have been used. In U.S. Pat. No. 5,518,377 to Bougamont et al, for instance, a stretchable rubber membrane has an end attached to the piston and serves as a return spring for the piston, biasing the piston upward. It also serves as a seal for the pump chamber as well as an intake check valve.
In pump dispensers there has always been a concern with a leak-resistant mounting of the pump on the container. In some cases this has been dealt with by annular sealing walls which have engaged the inside of the container finish. Most, however, have provided a liner or separate annular gasket which have been squeezed between the top wall of the container closure and the top of the finish of the container as the closure is screwed down tight.